Left ventricular (LV) diastolic dysfunction is characterized by abnormal myocardial mechanical properties that include impaired diastolic distensibility, impaired LV filling, and slow or delayed myocardial relaxation. Diastolic dysfunction is an increasingly prevalent clinical problem that is a major cause of congestive heart failure. Diagnosing diastolic dysfunction remains difficult and controversial. Conventional echocardiographic techniques are limited in their ability to provide a global assessment of diastolic function. 3D magnetic resonance imaging (MRI) with tissue tagging provides a geometry independent measure of LV torsion/twist, which determines shortening and relaxation of the myocardium. Here we introduce a novel concept called 'Torsional Hysteresis' that provides a comprehensive global assessment of LV diastolic function. Contraction of myocardial bundles and their interaction with extracellular matrix during systole results in storage of torsional potential energy. Torsional recoil during isovolumic relaxation and early diastole releases the potential energy stored in the deformed matrix during systole and thus is also dependent on systolic function. We have found that the torsion hysteresis defined as the area within torsion- volume loop is increased in patients with hypertension with diastolic dysfunction and preserved systolic function compared to patients with highly compliant LV of isolated mitral regurgitation and normal controls. Moreover, we have found that torsional hysteresis is not altered in progressive mitral regurgitation with progressive systolic dysfunction in a canine model of mitral regurgitation or in mitral valve repair in humans with isolated mitral regurgitation and preserved systolic function. Thus, we hypothesize that torsional hysteresis calculated from a 3-dimensional MRI with tagging provides a measure of diastolic function that reflects the viscoelastic properties of the myocardium independent of load. We propose to test this hypothesis in normal subjects and in patients with suspected diastolic dysfunction. PUBLIC HEALTH RELEVANCE: Diastolic Dysfunction is an increasingly prevalent clinical problem that is a major cause of congestive heart failure. Accurate diagnosis of diastolic dysfunction using non-invasive tools remains a challenge. Here we have proposed a novel clinically relevant non-invasive parameter called torsional hysteresis for the global assessment of diastolic function.